Flavobacterium columnare formally known as Flexibacter columnaris as well as Bacillus columnaris, and Cytophaga columnaris. This is a common gram-negative bacteria which gives the appearance of white fungus on fish but is actually a bacteria. Its name is derived from columnar shaped bacteria, which are present in virtually all aquarium environments.

If left untreated it is usually fatal and is highly contagious. A tank that has had columnaris in it should be completely restarted and cleaned out after an outbreak if all fish have been lost. This disease can be spread easily between tanks from contaminated fish nets, your own hands if they have not been washed in-between tanks, shared containers and even food.

Columnaris is partly caused by bad water quality, allowing uneaten food to remain in the tank causing this bacteria to multiply, as well as the fish having an inadequate diet or stressed from being introduced to a new tank. Wounds and injuries can easily become infected by this opportunist bacteria.

Cotton-wool-like mouldy growths around the mouth, similar to Mouth Fungus

Swelling of the kidneys, behind the gill/throat area

Fin and Tail Rot

Stringy Fungus appearance around the affected skin, often misdiagnosed as Fungus not Columnaris

White spots around the head, edges of fins and scales

It is important to note that there are a few strains of Columnaris that are extremely virulent and can cause death without any symptoms. The victim will usually be swimming as normal, then a minute later it will have what appears to be a seizure and drop dead after 10-30 seconds. If your fish suddenly die in this manner then Columnaris cannot be ruled out, and if it is happening to multiple fish in quick succession then it is almost certainly Columnaris. In these cases the best thing you can do is proceed with the treatment suggested below and hope that a few of your fish survive to tell the tale.

20% weekly water change, good biological filtration, maintaining good water quality, include vacuuming the substrate, keep tank well aerated, varied diet and not overstocked.

This is a quick acting disease and needs immediate treatment. Be aware that some strains of this bacteria are becoming resistant to antibiotics. So ensure you treat for the full length of the medication.